1. Field of the Invention
The present invention relates to mobile communication technologies. More particularly, the present invention relates to a method for positioning a Mobile Station (MS).
2. Background of the Invention
Along with an increase in requirements of information services based on position, wireless positioning techniques are becoming a focus of research. In a conventional cellular mobile communication network, the most commonly-used wireless positioning method is a Time Difference of Arrival (TDOA) method. In the TDOA method, a Mobile Station (MS) performs positioning by using signals of at least three cells. A time difference between arrivals of signals from any two cells is calculated and the position of the MS is determined according to the time difference. In this method, the MS need not know a specific time of signal transmission, and common errors generated due to channels can be eliminated or reduced. However, because signals of a serving cell are much stronger than signals of a neighboring cell, the stronger signals of the serving cell will create interference with the signals of the neighboring cell. As a result, there is a larger positioning error. In addition, in the E911 specification, at least 67% of positioning errors within one cell should be within 50 meters and at least 95% of positioning errors within one cell should be within 150 meters. However, the positioning errors in the TDOA method cannot meet the positioning requirements in the E911 specification, which is illustrated in the positioning error curve obtained by the TDOA method in FIG. 1.
FIG. 1 is a schematic diagram illustrating a positioning error curve obtained by a TDOA method in the conventional art.
Referring to FIG. 1, to address the above problem, the conventional art further proposes a method for establishing a Location Based Services (LBS) zone. The first subframe of a frame is taken as the LBS zone used for transmitting a reference signal of the neighboring cell, i.e. all time-frequency resources of the first subframe are used for transmitting the reference signal of the neighboring cell, and thus the MS can perform positioning according to the reference signal of each neighboring cell in the LBS zone received. Although this method can effectively restrain the interference of the signals of the serving cell on the signals of the neighboring cell and can increase positioning precision, this method will greatly affect Hybrid Automatic Repeat Request (HARQ) timing synchronization, and even more greatly in the case where the proportion of uplink subframes to downlink subframes in one frame is 4:4. In addition, with respect to a Time Division Duplexing (TDD) system, because the first subframe of a frame is completely taken as the LBS zone used for transmitting the reference signal of the neighboring cell in this method, uplink resources may not be allocated to a terminal, which greatly affects allocation and scheduling of system resources and disturbs normal operations of the TDD system.